I am trying to apply this upgrade, but keep getting the same error.
The file that is mentioned has not been removed/renamed or any other modifications done to it.
Upgrade 4.3.3 - 4.3.3.SP1
Validation issue
Validator "Restore" returned fail status
Unable to prepare restore.php file. File "var/upgrade/restore.php" was locally modified/renamed/removed. Restore the original restore.php file before the upgrade.
There should be a few posts about this issue. You may need to seasrch
You probably need to address ownership/permission issues.
First fix perms in config.local.php to be dirs = 755 and files = 644.
Then change all the dirs/file modes to those values in the var directory (and the var directory itself).
Then verify that all the ownerships are correct.
Rerun the upgrade. You didn't mention explcitly, but I assume the restore.php file exists. I had a site where it didn't and everything I tried failed including restoring it from the archive of the release that was to be upgraded.